A lot of technologies in which an inner liner having a low air permeability to reduce a thickness of a gauge thereof for the purpose of reducing a fuel consumption and decreasing a weight of a tire have so far been proposed.
Capable of being provided is, for example, a rubber composition for an inner liner having a low air permeability by blending a rubber composition for an inner liner with a polyamide base resin or a low air-holding thermoplastic resin. However, the problems that the bending resistance and the low temperature fatigue resistance are limited and that the versatility is poor have been involved in the above method.
On the other hand, known as filling materials of a rubber composition for an inner liner are:
1) a rubber composition for an inner liner prepared by blending 100 parts by weight of a rubber component with 10 to 50 parts by weight of tabular mica having an aspect ratio of 50 to 100 (refer to, for example, patent document 1), and
2) a rubber composition for an inner liner containing 100 parts by weight of a rubber component containing 20 to 50 parts by weight of diene base rubber and 50 to 80 parts by weight of halogenated butyl rubber, and 30 to 50 parts by weight of clay having an aspect ratio of 30 or more as a white filler (refer to, for example, patent document 2). However, there have been involved therein the problems that when the filler is increased in an amount, it is not uniformly dispersed by kneading rubber and that inferior dispersion thereof is liable to bring about a reduction in the bending resistance.
On the other hand, there have so far been known as a technology for improving a processability and the like in white filler-blended rubber compositions prepared by using glycerin fatty acid esters and the like, for example: 3) a rubber composition improved in an electrostatic property which is prepared by blending 100 parts by weight of a rubber containing 90 parts by weight or more of a diene base rubber with 30 to 120 parts by weight of a filler containing 40% by weight or more of a white filler and 0.2 to 8 parts by weight of a nonionic surfactant (refer to, for example, patent document 3), and
4) a rubber composition for a tire tread containing at least one polymer selected from the group of diene rubbers, and 5 to 100 parts by weight of fine powder non-precipitated silicic acid, 0 to 80 parts by weight of carbon black, and 0.5 to 20 parts by weight of at least one non-aromatic viscosity-reducing substance each based on 100 parts by weight of a rubber contained in the rubber composition, wherein the non-aromatic viscosity-reducing substance described above is at least one substance selected from the group consisting of glycerin monostearate, sorbitan monostearate, sorbitan monooleate, and trimethylolpropane(2-ethyl-2-hydroxymethyl-1,3-propanediol) (refer to, for example, patent document 4).
In the patent document 3 out of the patent documents 3 and 4, an effect of preventing electrification different from the present invention which can be brought about in blending glycerin fatty acid monoester and silica is described in one of the examples, but an effect of enhancing a dispersibility of a stratified or tabular clay mineral to improve a low air permeability and a bending resistance of the tire is neither described nor suggested therein.
Also, an effect of reducing a viscosity in blending silica by blending glycerin fatty acid monoester is described in the patent document 4 described above, but an effect of enhancing a dispersibility of a stratified or tabular clay mineral to improve a low air permeability and a bending resistance of the tire is neither described nor suggested therein.